1. Technical Field of the Invention
The present invention relates to a method of and apparatus for extracting abnormal factors in a processing operation for analyzing the causes of decline in the yield of products due to defects in producing apparatuses and conditions.
2. Description of Related Art
Generally, in a processing operation such as a diffusion process in a semiconductor producing plant, data on producing apparatus histories, producing conditions, and in-line measurement values are collected and stored, and in a following inspection process, data on quality results of products such as the yield of products and their electric characteristics are collected and controlled.
There has been no effective means for analyzing the causal relation between the product quality results information and other information which affects the quality of products such as apparatus history data, producing conditions and in-line measurement values. When it is detected that the yield is declining in the inspection process, an operator has to spot the cause by guesswork based on his experience, which may be not always correct.
There have thus been a need of providing a method for detecting the causes of decline in quality of products at an early stage. Although some methods using a known multivariate analysis method have actually been tried, they still have such disadvantages as described hereinafter.
Firstly, as there are too many items for making an explanation of the variables, the results can hardly reflect actual conditions. Secondly, when producing many kinds of products in a small amount, the quantity of data is much too little for conducting proper analysis. Thirdly, the time required for searching the desired data to explain the causes and for preliminarily processing data to cover missing data prevents an early solution of the causes. Fourthly, the operator is required to have thorough knowledge of a multivariate analysis method, and thus not everyone can easily utilize the method.